Limit switch system



Aug. 20, 1946.

J. A. CHILMAN LIMIT SWITCH SYSTEM Filed Feb. 2, 1945 2 Sheets-Shet 1 Jo/m /5 /ulzinan jnunzbr 1946- J. A. CHILMAN LIMIT SWITCH SYSTEM 2Sheets-Sheet 2 Filed Feb. 2, 1943 Patented Aug. 20, 1946 signorto RotolLimit ed, a British company 'Application February 2, 1943, Serial No.474,449 In Great Britain December 22, 1941 3 Claims. 1

I This invention concerns improvements in .or relating to variable-pitchpropellers of the kind in :which-the pitchachangin'g movement of theblades 'is effected by. electric motor carried .ontheZhub-o'f thepropeller. In the simplest kind of variable-pitch propeller, the pitchis adjustable between a fine-pitch .setting and a coarse- .pitchsetting, but it is also desirable that a vfurther range of adjustmentshould be provided to enable the blades to be feathered, and in recentdevelopments, the range has been still further extended to enable thepitch to be reversed. Furthermore, .it .is desirable, and is alreadyknown, to provi'de for automatic or manual control of the adjustment :ofthe pitch, :the automatic control being used for making such adjustmentsas will maintain the engine-speed constant, whilst the manual control isused for feathering, reversing, or for adjustment of the pitch when. theautomatic control :is cut out. It is also desirable to providelimit-switches or cut-outs automatically operated by the blade when itreaches a limiting position in any of its adjusting movements in orderto simplify the operational control.

It is an object of the present invention to provide an improvedarrangement of controlling circuits when a three-phase alternatingcurrentsupply is used, and to enable any or all of the above controlarrangements to be obtained with the minimum number of connections tothe mo- 5 tor. The importance f reducing the number of connections liesin the fact that the motor is mounted on the propeller-hub and rotatestherewith so .that separate slip-rings are necessary for each separateconnection to it.

According to this invention, an alternating currentelectrically-operated variable pitch propeller comprises a three-phasepitch-changing motor, and not more than four slip-rings providingconnections therefrom to control-switches whereby anyof'the operationalcontrols above set forth may be effected.

The invention also-comprises in an alternating currentelectrically-operated variable-pitch pro- 1 pe'ller as above set forth,the arrangement wherein one phase winding of the motor is connected totwo automatic cutouts whichare in parallel with one another and areconnected through a two-way selector-switch .to one phase of the supply,a solenoid operated' switch having two alternative operating-windingsconnected respectively in the lines between said selector switch andsaid cutouts, and a reversing-switch for two phases of the supply,one-of the outputlines of said are connected to one reversing-switchhaving the solenoid-operated switch in it.

Preferably the automatic cut-outs aforesaid phase of the supply and thereversing-switch in the other two phases of the supply, and with thisarrangement only four slip-rings are necessary for the motorconnections.

According to another feature of this invention, one of the automaticcut-outs aforesaid is arranged to be operated in the two limitingpositions. of the range of movement of the blade, suchjfor example, asthe reverse position and the feather position, and the other cut-out isarranged to be operated at some intermediate .position-suchfor example,:as the limitim finepitch position for normal operation of the.propeller. The advantage of this arrangement is that when the propelleris being returned from its reverse position, it is automatically stoppedon reaching the said fine-pitch cut-out and the automatic control canthen take charge if so desired. It will be appreciated, however, thatfor this purpose any other suitable position for thesintermediatecut-out could be used, such, for example, as the maximum coarse-pitchposition for automatic working, but it is preferred to use thefine-pitch position for this cut-out.

In the accompanying drawings,

Figure l is a simplied drawing of so much of an electrically-operatedvariable pitch propeller as is necessary for the understanding of thisinvention,

Figured! is a diagram of the cont ol circuits,

' and Figure 3 is a diagram of an alternative arrangement of controlcircuits.

Referring to these drawings, the propeller comprises a hub it which ismounted on the shatt of an engine indicated at 1 I to be driven thereby.and has blades 52 mounted in it so as to be variable as to their pitch.The pitchchanging movements are effected by an electric motor suitablereduction gear contained 'in a housing the reduction gear drivin abevelwheel M which meshes in the usual manner with similar gears mountedone on the root end of each of the blades.

The-electric supply to the motor, which it will be appreciated isrotating with the propeller, is effected by means of slip-rings l5mounted on the driving shaft within a housing 15 secured to thecrankcase of the engine. Contact with these slip-rings is "made by meansof brushes I! mounted .on a carrier 18., which, in Figure 1, is

shown as displaced, but is inserted through a suitable opening in thecasing l6.

From each of these slip-rings l an insulated conductor l9 extendsthrough the hub l8 to a contact member 29, and similar contact membersare mounted on the casing |3 to mate with them, so that the completemotor with its reduction gear, and other associated parts, can bedetached as a unit. In the case of two of these conductors, the matingcontact 2| is springpressed forward and associated with a cam-operatedbellcrank lever 22 to constitute a limit switch or automatic cut-out;the lever 22 is operated by a suitable cam or cams rotatable with thegear I4, and the object of this construction is to provide an automaticcut-out at certain Pitch positions of the blades as hereinafterdescribed. Automatic cut-outs of this kind are used on variable-pitchpropellers which have a direct current pitch-adjusting electric motor.

In the present invention, a three-phase alternating current motor isused as the pitch-changing motor and this is shown in the circuitdiagram Figure 2 with the three-phases 23, 24, 25 star connected. It isdesirable to use a springloaded brake in association with the motor tohold it stationary, and a three-phase electromagnet 29 is connected inparallel with the motor for the purpose of releasing the brake, whenevercurrent is supplied to the motor to operate Two of the phases 23, 24 areconnected directly to the slip-rings l5 of Figure 1, the position ofwhich is indicated at 21 in the circuit diagram Figure 2, and the thirdphase 25 is connected to two automatic cut-outs 28, 29, which correspondto the contacts 28, 2| of Figure 1. These two cut-outs 28, 29 areconnected in parallel with one another and to their respectiveslip-rings, and the cut-out 28 is arranged to be automatically openedwhen the blades reach either their feathered position or their reverseposition. The cutout 29 is arranged to be opened at any suitableintermediate position in the range of travel of the blades, and ingeneral it is convenient that this position should be a limitingfine-pitch position for normal working conditions.

From the four slip-rings, one line 38 is taken to one pole of areversing switch indicated generally by the reference 34; the secondline 3| is taken through an electromagnetically-controlled switch 35 tothe other pole of the reversing switch 34; the two remaining lines 32,33 are taken through solenoids 36, 31 either of which when energisedcloses the normally open switch 35. These two lines 32, 33 are continuedto two contacts of a two-Way selector switch 38.

The three-phase supply has two of its lines 39, 48 connected to thereversing switch 34, and the third line 4| connected to the two-wayselector switch 38.

It will be seen that the function of the reversing switch 34 is tointerchange the power supply lines 39, 48 with the two lines 39, 3|which are connected to the two phases 23, 24 of the motor, and that theselector switch 38 in either of its closed positions connects the supplyline 4| to the phase 25 of the motor. The throwing over of the reversingswitch 34 from one position to another, by reversing the two phases 23,24, reverses the direction of rotation of the motor.

The operation of the controls will now be described. Assuming that thereversing switch 34 and the selector switch 38 are both open, if it isdesired to adjust the blades towards a coarserpitch position, thereversing switch 34 is closed, say to the position shown in Figure 2, toselect the desired direction of rotation of the motor and the switch 38is closed on to the line 33 so that a circuit is provided through thecut-out 28 to the motor, it being appreciated that the cutout 28 isclosed in all positions except when the blades reach their reverse orfeathered positions. The closing of the switch '38 energises the coil 31and therefore closes the switch 35 so as to complete the circuit of theline 3| so that all three phases of the supply are connected to themotor and it is set in rotation in the appropriate direction to coarsenthe pitch of the blades. If it is merely desired to make a smalladjustment, the operation can be stopped by opening the switch 38. Thisdisconnects the supply line 4| from the motor, and the coil 31 istherefore no longer energised, so that the switch 35 opens, whichdisconnects the supply line 39 from the motor; two of the phases beingthus opened, the motor stops and the brake is automatically applied.

If it be desired to feather the blades, the setting of the switches 34and 38 above described, that is to say the setting ilustrated in Figure2, is allowed to stand until the blades reach their feathered position.At this point the cut-out 28 is automatically opened, therebydisconnecting the supply line 4|, de-energising the coil 31, opening theswitch 35 and disconnecting the supply line 39 so that two phases beingopened, the motor stops.

Starting again from the original setting with the two switches 34, 38both open, if it is desired to adjust the blades to a finer-pitchsetting, the reversing switch 34 is thrown over so as to reverse thedirection of rotation of'the motor, and the switch 38 is closed. on tothe line 32. This energises the coil 38 and closes the switch 35 so thatall three phases are now connected to the motor and it rotates in theappropriate direction, the circuit through the cut-out 29 being normallyclosed. If this movement be allowed to continue, the cut-out 29 isopened when the blades reach their limiting fine-pitch position fornormal working, so that the supply to phase 25 of the motor isinterrupted, the coil 35 is deenergised and the switch 35 isautomatically opened So that the second phase of the supply to the motoris opened, and the motor thereupon stops.

The setting of the switches for adjusting the blades to a finer pitch isalso used for returning them from their feathered position which wasattained as above described. In attaining the feathered position, theswitches 34, 38 were arranged as shown in Figure 2, and at the featheredposition the cut-out 28 was automatically opened. To return the bladesfrom this position, the switches 34, 38 are set as above described foradjustment to a finer-pitch setting. The switch 38 is now connectedthrough the line 32 to the cut-out 29 which is closed since the bladeshave been moved past the normal fine-pitch position. The motor istherefore set in rotation bringing the blades towards their normalfine-pitch setting and on reaching that point the cut-out 29 is openedso that further control ceases. Any further adjustment may be effectedmanually, or automatically as hereinafter described.

If it be desired to adjust the blades to their reverse-pitch position,this is effected by setting the reversing switch 34 to give theappropriate direction of rotation to the motor (which is the same as forobtaining a finer-pitch as above described), but the switch 38 isconnected to the line 33 so that the circuit is taken through thecut-out 28 instead of through the cut-out 29 which opens automaticallyat the normal finepitch setting. The adjusting movement of the bladestherefore continues beyond the normal fine-pitch setting until thecut-out 28 is opened automatically on reaching the reverse position.

For the purpose of returning from the reversepitch position of theblades, the switch 34 is set for the appropriate direction of rotation,which is that of coarsening the pitch, and the switch 38 is connected tothe line 32 so that the circuit is completed through the cut-out 29which is closed when the blades are in their reverse position. The motoris thereby set in rotation and continues until the cut-out 29 is openedautomatically, if the adjustment is not interrupted before that point isreached by manually opening the switch 38.

It is customary to provide on yariable-pitch propellers an automaticgovernor-operated control for maintaining the engine-speed constant bymaking suitable adjustments in the pitch of the blades, increasing it asthe engine-speed tends to rise and decreasin it as the speed tends tofall. Mechanism for this purpose is well-known, and may be arranged tooperate through relay switches connected to the supply side of thesolenoid-controlled switch 35, such switches performing equivalentoperations t those above described for adjustment towards fine-pitch ortowards coarse-pitch respectively.

It will be seen that the above described arrangement of control circuitsenables all the required controlling operations to be eil'ected on thepitch-changing motor whilst using only four slip-rings for connectionwith the motor and this is of importance as any increase in the numberof slip-rings usually involves an undue increase in the overalldimensions of the installation.

In Figure 3 there is illustrated a modified arrangement comprising areversing switch 42 for interchanging two phases 43, 44 of the supply.The third phase 45 is shown as directly connected to one phase of themotor 46. The selectorswitch 41 corresponding to the switch 38 of Figure2' is connected in series with the reversing switch 42, bein connectedto the output line thereof which is not connected to thesolenoidoperated switch 48 corresponding to the switch 35 of Figure 2.The general mode of operation of this system is similar to thatdescribed with reference to Figure 2, but it ofiers the advantage thatsince the supply line 45 is directly connected to the motor, one of theslip-rings could, if desired, be omitted, thereby reducing the number tothree, the connection being made by earthing the phase 45 of the supplyand the corresponding phase of the motor. In some installations it isconsidered undesirable to earth one phase of the supply so that thisarrangement is of a more limited application than the arrangement shownin Figure 2.

In the arrangement according to this invention, the full range ofcontrol of the pitch from reverse to feathering positions is provided,but in some instances lesser ranges of adjustment may be sufiicient andthese are provided principally by a suitable design or selection of thecut-outs 28, 29. Thus, for example, if the reverse setting of the bladesof a propeller is not required, the cut-out 28 which as described aboveis opened at both the feathered and reverse positions, may be arrangedto operate only in the featherin position; also it may be desired toprovide an automatic stop at the coarse-pitch limit of the normalworking range, and this would be provided on the cut-out 29. In thiscase the switch 38 would normally be connected to the line 32 of Figure2 and would be connected to the line 33 only for the purpose offeathering. Similarly any other desired arrangement of cut-out can beused to suit any particular requirements, with appropriate modificationsin the operation of the switches.

I claim:

1. In combination with a three-phase motor, and a three-phase supplyline for the motor, of a control comprising a normally open e1ectro-Inagnetic switch connected to one phase of the motor, a reversing switchconnected to another phase of the motor and to said electromagneticswitch and also to two of the lines of the supply for reversing themotor, a two way selector switch connected to the third line of thesupply, two circuits connecting said selector switch with the thirdphase of said motor, a limit switch and a coil of said electromagneticswitch bein in each of said circuits whereby closing of either circuitby said selector switch will cause closing of the electromagneticswitch.

2. Controlling means for a three-phase electric reversible motorcomprising in combination three feed lines of a three-phase electricpower supply, a, reversing switch connected to two of said feed lines, asupply line from one output terminal of said reversin switch, a secondsupply line from the second output terminal of said reversing switch, asolenoid-operated switch in said second supply line, a two-way selectorswitch connected to the third feed line, two solenoids connectedrespectively to the output terminals of said selector switch, saidsolenoids being alternatively operable to close said solenoid-operatedswitch, connections from each of said solenoids to a third supply line,and means for connecting said three supply lines respectively to thethreephase-terminals of a motor.

3. Controlling means for a three-phase electric reversible motorcomprising in combination three feed lines of a three-phase electricsupply, means for connecting one of said feed lines with onephase-terminal of a three-phase motor, a reversing switch connected tothe second and third feed lines, a supply line from one output terminalof said reversing switch and means for connecting it to the secondphase-terminal of a three-phase motor, a solenoid-operated switch insaid line, a line from the second output terminal of said reversingswitch to a two-way selector switch, lines from the two output terminalsof said selector switch, a solenoid in each of said lines, saidsolenoids being alternatively operative on said solenoid-operatedswitch, a line from each of said solenoids connected to a third supplyline, and means for connecting said third supply line to the thirdphase-terminal of a three-phase electric motor.

JOHN ALFRED CHILMAN.

